WebSockets for Django
… image:: https://secure.travis-ci.org/stephenmcd/django-socketio.png?branch=master
:target: http://travis-ci.org/#!/stephenmcd/django-socketio
Created by Stephen McDonald <http://twitter.com/stephen_mcd>_
django-socketio is currently bound to socket.io 0.6, which is considerably
out of date. It’s fully functional, but some browsers now have newer
implementations of WebSockets, and so alternative socket.io transports are
fallen back to in these cases.
Work is currently underway to bring django-socketio up to date with the
latest gevent-socktio, which has just recently started to support
socket.io 0.8
Follow this thread for more info:
https://github.com/stephenmcd/django-socketio/issues/19
django-socketio is a BSD licensed_ Django_ application that
brings together a variety of features that allow you to use
WebSockets_ seamlessly with any Django project.
django-socketio was inspired by Cody Soyland’s introductory
blog post on using Socket.IO_ and gevent_ with Django, and
made possible by the work of Jeffrey Gelens'_ gevent-websocket_
and gevent-socketio_ packages.
The features provided by django-socketio are:
PyPI_signals_-like event system that abstracts away the variousPrior to version 0.3, the message argument sent to each of the event
handlers was always a Python list, regardless of the data type that
was used for sending data. As of 0.3, the message argument matches the
data type being sent via JavaScript.
Note that if you’ve never installed gevent, you’ll first need to
install the libevent development library. You may also need the Python
development library if not installed. This can be achieved on Debian
based sytems with the following commands::
$ sudo apt-get install python-dev
$ sudo apt-get install libevent-dev
or on OSX using Homebrew_ (with Xcode installed)::
$ brew install libevent
$ export CFLAGS=-I/brew/include
or on OSX using macports::
$ sudo port install libevent
$ CFLAGS="-I /opt/local/include -L /opt/local/lib" pip install django-socketio
The easiest way to install django-socketio is directly from PyPi using
pip_ by running the following command, which will also attempt to
install the dependencies mentioned above::
$ pip install -U django-socketio
Otherwise you can download django-socketio and install it directly
from source::
$ python setup.py install
Once installed you can then add django_socketio to your
INSTALLED_APPS and django_socketio.urls to your url conf::
urlpatterns += [
url("", include('django_socketio.urls')),
]
The client-side JavaScripts for Socket.IO and its extensions can then
be added to any page with the socketio templatetag::
<head>
{% load socketio_tags %}
{% socketio %}
<script>
var socket = new io.Socket();
socket.connect();
// etc
</script>
</head>
The runserver_socketio management command is provided which will
run gevent’s pywsgi server which is required for supporting the type of
long-running request a WebSocket will use::
$ python manage.py runserver_socketio host:port
Note that the host and port can also configured by defining the following
settings in your project’s settings module:
* ``SOCKETIO_HOST`` - The host to bind the server to.
* ``SOCKETIO_PORT`` - The numeric port to bind the server to.
These settings are only used when their values are not specified as
arguments to the runserver_socketio command, which always takes
precedence.
… note::
On UNIX-like systems, in order for the ``flashsocket`` transport
fallback to work, root privileges (eg by running the above command
with ``sudo``) are required when running the server. This is due to
the `Flash Policy Server`_ requiring access to a `low port`_ (843).
This isn't strictly required for everything to work correctly, as
the ``flashsocket`` transport is only used as one of several
fallbacks when WebSockets aren't supported by the browser.
When running the runserver_socketio command in production, you’ll
most likely want to use some form of process manager, like
Supervisor_ or any of the other alternatives.
The WebSocket implemented by gevent-websocket provides two methods for
sending data to other clients, socket.send which sends data to the
given socket instance, and socket.broadcast which sends data to all
socket instances other than itself.
A common requirement for WebSocket based applications is to divide
communications up into separate channels. For example a chat site may
have multiple chat rooms and rather than using broadcast which
would send a chat message to all chat rooms, each room would need a
reference to each of the connected sockets so that send can be
called on each socket when a new message arrives for that room.
django-socketio extends Socket.IO both on the client and server to
provide channels that can be subscribed and broadcast to.
To subscribe to a channel client-side in JavaScript use the
socket.subscribe method::
var socket = new io.Socket();
socket.connect();
socket.on('connect', function() {
socket.subscribe('my channel');
});
Once the socket is subscribed to a channel, you can then
broadcast to the channel server-side in Python using the
socket.broadcast_channel method::
socket.broadcast_channel(“my message”)
Each server-side socket instance contains a handful of methods
for sending data. As mentioned above, the first two methods are
implemented by gevent-socketio_:
socket.send(message) - Sends the given message directly tosocket.broadcast(message) - Sends the given message to allThe remaning methods are implemented by django-socketio.
socket.broadcast_channel(message, channel=None) - Sends thesocket.send_and_broadcast(message) - Shortcut that sends thesocket.send_and_broadcast_channel(message, channel=None)
The following methods can be imported directly from
django_socketio for broadcasting and sending out-of-band (eg: not
in response to a socket event). These methods map directly to the same
methods on a socket instance, and in each case an appropriate connected
socket will be chosen to use for sending the message, and the
django_socketio.NoSocket exception will be raised if no connected
sockets exist.
django_socketio.broadcast(message)django_socketio.broadcast_channel(message, channel)django_socketio.send(session_id, message)Note that with the send method, the socket is identified by its
session ID, accessible via socket.session.session_id. This is a
WebSocket session ID and should not be confused with a Django session
ID which is different.
The django_socketio.events module provides a handful of events
that can be subscribed to, very much like connecting receiver
functions to Django signals. Each of these events are raised
throughout the relevant stages of a Socket.IO request. These events
represent the main approach for implementing your socket handling
logic when using django-socketio.
Events are subscribed to by applying each event as a decorator
to your event handler functions::
from django_socketio.events import on_message
@on_message
def my_message_handler(request, socket, context, message):
...
Where should these event handlers live in your Django project? They
can go anywhere, so long as they’re imported by Django at startup
time. To ensure that your event handlers are always loaded, you can
put them into a module called events.py in one of your apps listed
in Django’s INSTALLED_APPS setting. django-socketio looks for these
modules, and will always import them to ensure your event handlers are
loaded.
Each event handler takes at least three arguments: the current Django
request, the Socket.IO socket the event occurred for, and a
context, which is simply a dictionary that can be used to persist
variables across all events throughout the life-cycle of a single
WebSocket connection.
on_connect(request, socket, context) - occurs once when theon_message(request, socket, context, message) - occurs everymessageon_subscribe(request, socket, context, channel) - occurs whenchannel argumenton_unsubscribe(request, socket, context, channel) - occurschannelon_error(request, socket, context, exception) - occurs whenexception argument whichon_disconnect(request, socket, context) - occurs once whenon_finish(request, socket, context) - occurs once when theLike Django signals, event handlers can be defined anywhere so long
as they end up being imported. Consider adding them to their own
module that gets imported by your urlconf, or even adding them to
your views module since they’re conceptually similar to views.
All events other than the on_connect event can also be bound to
particular channels by passing a channel argument to the event
decorator. The channel argument can contain a regular expression
pattern used to match again multiple channels of similar function.
For example, suppose you implemented a chat site with multiple rooms.
WebSockets would be the basis for users communicating within each
chat room, however you may want to use them elsewhere throughout the
site for different purposes, perhaps for a real-time admin dashboard.
In this case there would be two distinct WebSocket uses, with the chat
rooms each requiring their own individual channels.
Suppose each chat room user subscribes to a channel client-side
using the room’s ID::
var socket = new io.Socket();
var roomID = 42;
socket.connect();
socket.on('connect', function() {
socket.subscribe('room-' + roomID);
});
Then server-side the different message handlers are bound to each
type of channel::
@on_message(channel="dashboard")
def my_dashboard_handler(request, socket, context, message):
...
@on_message(channel="^room-")
def my_chat_handler(request, socket, context, message):
...
The following setting can be used to configure logging:
* ``SOCKETIO_MESSAGE_LOG_FORMAT`` - A format string used for logging
each message sent via a socket. The string is formatted using
interpolation with a dictionary. The dictionary contains all the
keys found in Django's ``request["META"]``, as well as ``TIME``
and ``MESSAGE`` keys which contain the time of the message and
the message contents respectively. Set this setting to ``None``
to disable message logging.
The “hello world” of WebSocket applications is naturally the chat
room. As such django-socketio comes with a demo chat application
that provides examples of the different events, channel and broadcasting
features available. The demo can be found in the example_project
directory of the django_socketio package. Note that Django 1.3 or
higher is required for the demo as it makes use of Django 1.3’s
staticfiles app.
… _BSD licensed: http://www.linfo.org/bsdlicense.html
… _Django: http://djangoproject.com/
… _WebSockets: http://en.wikipedia.org/wiki/WebSockets
… _Cody Soyland: http://codysoyland.com/
… _blog post: http://codysoyland.com/2011/feb/6/evented-django-part-one-socketio-and-gevent/
… _Socket.IO: http://socket.io/
… _Jeffrey Gelens': http://www.gelens.org/
… _gevent: http://www.gevent.org/
… _gevent-websocket: https://bitbucket.org/Jeffrey/gevent-websocket/
… _gevent-socketio: https://bitbucket.org/Jeffrey/gevent-socketio/
… _PyPI: http://pypi.python.org/
… _signals: https://docs.djangoproject.com/en/dev/topics/signals/
… _Homebrew: http://mxcl.github.com/homebrew/
… _pip: http://www.pip-installer.org/
… _Supervisor: http://supervisord.org/
… _Flash Policy Server: http://www.adobe.com/devnet/flashplayer/articles/socket_policy_files.html
… _low port: http://www.staldal.nu/tech/2007/10/31/why-can-only-root-listen-to-ports-below-1024/